Why are so many of these sentences weird? I was doing dutch and got the sentence "I am not a banana!" and also "Luis eats spiders" in spanish.
I don't really have an answer for you, but I found that out too. They have such weird sentences. But I guess maybe they want you to laugh or shake your head? I find some of them hilarious. :)
I've gotten a few as well and I wish there were more! Not only does it help me remember the words/grammar, I feel more of an accomplishment when I translate a weird sentence correctly because I know I know the words/grammar and I'm not just on autopilot.
I think that's an important point – if all the sentences were of the type 'where is the hotel' then there will be greater tendency to just guess them.
Also, the publicity they get from sentences being shared on social media helps them. For example: Zooey Deschanel (New Girl) tweeting about 'You are easy' etc. In fact the job advert for Duolingo Stories/Bots had a reference to this aspect.
I was just listening to a Podcast on the language instruction system called TPRS ("Teaching Proficiency through Reading and Storytelling"). Using unexpected sentences was explicitly mentioned as a useful part of the system. As others have said, it's because they're more memorable.
Also, yes, there are plenty of weird sentences on Duolingo. A search through the forum will show some of these sentences.